The present invention relates to tensioners for tensioning engine driven elements such as timing belts or chains. In particular, the present invention is primarily concerned with timing belt tensioners, although the principles of the present invention may also be applied to accessory belt and chain tensioners and timing chain tensioners.
In prior art tensioners, the tensioner geometry and characteristics of the tensioner""s spring are selected to ensure that the belt tension required to move the tensioner through its range of operating positions remains relatively constant throughout the range. That is, these tensioners are designed so that as belt tension increases due to engine conditions, such as thermal expansion or increased operational belt loads, the tensioner moves under the increased belt tension to compensate for such increases and maintain the belt tension relatively constant.
Prior art tensioners are normally provided with a pair of stops, one at the maximum travel position of the tensioner arm and one at the free arm position of the tensioner arm. These stops restrict the pivotal movement of the tensioner arm and provide the same with a limited range of movement. Because the belt tension required through the range is relatively constant, increases in belt tension can cause the tensioner arm to travel through the range of operating positions until tensioner arm contacts the stop at the maximum travel position thereof. When the increase in belt tension is rapid, the contact between the tensioner arm can create undesirable noises or, in the worst case scenario, damage-the tensioner. This type of increase occurs most commonly as a result of engine kickback at shutdown. If the tensioner is damaged, the engine itself may suffer extensive damage as a result of the timing belt or chain failing to operate the component(s) connected thereto in proper timing with respect to the engine cycles.
Consequently, there exists a need in the art for a tensioner that can be used in combination with vehicle engine that eliminates the problems discussed above with respect to prior art tensioners.
It is an object of the present invention to meet the above-described need. To achieve this object, one aspect of the present invention provides a combination comprising a vehicle engine, an endless flexible driving element driven by the engine, and a tensioner. The tensioner comprises a fixed structure mounted on the engine, a pivot structure pivotally mounted on the fixed structure for pivotal movement about a pivot axis, spring structure constructed and arranged to apply a tensioning torque to the pivot structure that tends to pivot the pivot structure in a tension applying direction, and a rotatable member rotatably mounted on the pivot structure for rotation about a rotational axis spaced radially from the pivot axis by a radius. The rotatable member engages the driving element in a tension applying relationship such that the driving element is tensioned and in reaction applies a hub load force to the rotatable member at an angle with respect to the radius.
The tensioner is mounted on the engine such that when the engine is in an initial condition the pivot structure is angularly positioned at an initial angular position spaced from a perpendicular angular position at which the hub load force would be applied to the rotatable member perpendicularly to the radius. The initial angular position is spaced from the perpendicular angular position in an opposite direction opposite the tension applying direction. In the initial angular position, the spring structure applies the tensioning torque to the pivot structure such that the driving element is tensioned to a first mean dynamic tension.
As the engine thermally expands to its hot engine condition, the mean dynamic tension in the driving element increases so that the hub load force applied by the driving element pivots the pivot structure in the opposite direction away from the initial angular position thereof to a hot engine angular position. In the hot engine angular position, the spring structure applies the tensioning torque to the pivot structure such that the driving element is tensioned to a second mean dynamic tension greater than the first mean dynamic tension. The tensioner is constructed and arranged such that, as the pivot structure is pivoted from the initial angular position thereof to the hot engine angular position thereof, the angle between the hub load force and the radius continually increases and the spring structure is continually increasingly stressed so that the mean dynamic tension in the driving element continually increases from the first mean dynamic tension to the second mean dynamic tension during the thermal expansion of the engine. The tensioner is also constructed and arranged such that the mean dynamic tension of the driving element required to continue pivoting the pivot structure in the opposite direction from the hot engine position thereof continually increases as a result of the angle between the hub load force and the radius continually increasing and the spring structure being continually increasingly stressed the further the pivot structure is pivoted in the opposite direction from the hot engine position.
The key feature to note of this aspect to the invention is that in the initial angular position of the pivot structure is spaced from the perpendicular angular position in the opposite direction. As a result, as the pivot structure is pivoted from the initial angular position thereof to the hot engine angular position thereof, the angle between the hub load force and the radius continually increases beyond 90 degrees and the spring structure is continually increasingly stressed so that the mean dynamic tension in the driving element continually increases from the first mean dynamic tension to the second mean dynamic tension during the thermal expansion of the engine. Likewise, the mean dynamic tension of the driving element required to continue pivoting the pivot structure in the opposite direction from the hot engine position thereof continually increases as a result of the angle between the hub load force and the radius continually increasing and the spring structure being continually increasingly stressed the further the pivot structure is pivoted in the opposite direction from the hot engine position. In prior art tensioners, the initial angular position of the pivot structure is spaced from the perpendicular angular position in the tension applying direction. Because the torque acting against the spring structure is related to the sine of the angle between the hub load force applied to the rotatable member and the radius, the sine of this angle increases as the pivot structure approaches the perpendicular angular position, thus maximizing the contribution of the tensioner""s geometry to that torque. By spacing the initial angular position of the pivot structure in the opposite direction from the perpendicular angular position, the contribution offered to that torque by the tensioner""s geometry is reduced, and this reduction increases as a function of the angle between the hub load force and the radius continuing to increase (and hence the sine of that angle decreasing).
In another way to achieve the object of the present invention, another aspect of the present invention provides a vehicle engine, an endless belt driven by the engine, and a tensioner. The engine is capable of applying a maximum tension to the driving element during operation thereof. This maximum tension is the known maximum tension which the engine is capable of creating, and is normally determined from either manufacturer specifications or testing.
The tensioner comprises a fixed structure mounted on the engine, a pivot structure pivotally mounted on the fixed structure for pivotal movement about a pivot axis within a range of angular positions, spring structure constructed and arranged to apply a tensioning torque to the pivot structure that tends to pivot the pivot structure in a tension applying direction within the range of angular positions, and a rotatable member rotatably mounted on the pivot structure for rotation about a rotational axis spaced radially from the pivot axis by a radius. The rotatable member engages the driving element in a tension applying relationship such that the driving element is tensioned and in reaction applies a hub load force to the rotatable member at an angle with respect to the radius. The range of angular positions of the pivot structure includes a potential tooth skip position. This potential tooth skip position is the point at which, if the pivot structure were moved into the potential tooth skip position under driving element tension and then the tension in the driving element were decreased, tooth skip would be allowed to occur between the driving element and the engine if the spring structure failed to move the pivot structure in the tension applying direction to maintain the rotatable member in the tension applying relationship with the driving element. It is important to understand that the tensioner in accordance with this aspect of the invention is designed to prevent the pivot structure from moving into this potential tooth skip position, and that the pivot structure does not necessarily have to move into this position during operation. Instead, this potential tooth skip position is a position at which such tooth skip would occur if the pivot structure were moved to that position and the spring structure failed to move the pivot structure in the tension applying direction. This failure can possibly occur from dirt and other particulate material jamming the pivot structure""s movement, or from water on the tensioner freezing during winter conditions and hence jamming the pivot structure""s movement.
The tensioner is constructed and arranged such that the mean dynamic tension of the driving element required to pivot the pivot structure in the opposite direction from the hot engine position thereof towards and into the potential tooth skip position is greater than the aforesaid maximum tension the engine is capable of applying to the driving element. Because the mean dynamic tension required to pivot the pivot structure into the potential tooth skip position thereof is greater than the maximum tension that the engine is capable of creating, the tensioner can be considered self-limiting and the need for a maximum travel stop can be obviated. It should be noted, however, that a maximum travel stop may be provided within this aspect of the invention as a safety feature in order accommodate for incorrect installations and the like.
In yet another way to achieve the object of the present invention, yet another aspect of the present invention provides a combination comprising a vehicle engine adapted to thermally expand from an initial condition at an ambient temperature to a hot engine condition due to an increase in engine temperature during engine operation; an endless flexible driving element driven by the engine; and a tensioner. The tensioner comprises a fixed structure mounted on the engine; a pivot structure pivotally mounted on the fixed structure for pivotal movement about a pivot axis; spring structure constructed and arranged to apply a tensioning torque to the pivot structure that tends to pivot the pivot structure in a tension applying direction; a maximum travel stop constructed and arranged to engage the pivot structure pivoting in an opposite direction opposite the tension applying thereof to thereby prevent further pivotal movement of the pivot structure in the opposite direction and provide the pivot structure with a maximum travel angular position; and a rotatable member rotatably mounted on the pivot structure for rotation about a rotational axis spaced radially from the pivot axis by a radius. The rotatable member engages the driving element in a tension applying relationship such that the driving element is tensioned and in reaction applies a hub load force to the rotatable member at an angle with respect to the radius.
The tensioner is mounted on the engine such that when the engine is in the initial condition the pivot structure is angularly positioned at an initial angular position. In the initial angular position, the spring structure applies the tensioning torque to the pivot structure such that the driving element is tensioned to a first mean dynamic tension when the pivot structure is in the initial angular position thereof. As the engine thermally expands to the hot engine condition, the mean dynamic tension in the driving element increases so that the hub load force applied by the driving element pivots the pivot structure in the opposite direction away from the initial angular position thereof to a hot engine angular position. In the hot engine angular position, the spring structure applies the tensioning torque to the pivot structure such that the driving element is tensioned to a second mean dynamic tension when the pivot structure is in the hot engine angular position thereof.
The spring structure and the initial angular position of the pivot structure are selected such that the mean dynamic tension of the driving element required to pivot the pivot structure in the opposite direction from the hot engine position to the maximum travel angular position continually increases in such a manner that the mean dynamic tension required to move the pivot structure from the hot engine position to the maximum travel position is at least 75% greater than the second mean dynamic tension. This feature effectively reduces the contact between the pivot structure and the maximum travel stop, unless the specified driving element tension is created. Further, in the event that the tension is high enough to create contact between the pivot structure and the stop, this increased resistance effectively xe2x80x9ccushionsxe2x80x9d the upstroke of the pivot structure and reduces the force with which such contact is made. In prior art tensioners, there is normally some slight increase in belt tension as the pivot structure moves beyond the hot engine angular position thereof. However, the goal in these prior art tensioners is to maintain a constant belt tension and the increase is not enough to have as significant of an effect as this aspect of the invention, wherein a 75% or greater increase over the second dynamic tension is required. The minimum threshold of 75% is where significant improvement in this type of behavior is typically, seen, and thus is to be regarded as a commercially valuable lower end for this range.
In still another way to achieve the object of the present invention, still another aspect of the present invention provides a combination comprising a vehicle engine adapted to thermally expand from an initial condition at an ambient temperature to a hot engine condition due to an increase in engine temperature during engine operation; an endless flexible driving element driven by the engine; and a tensioner. The tensioner comprises a fixed structure mounted on the engine; a pivot structure pivotally mounted on the fixed structure for pivotal movement about a pivot axis within a predetermined range of angular positions; spring structure constructed and arranged to apply a tensioning torque to the pivot structure that tends to pivot the pivot structure in a tension applying direction within the predetermined range of angular positions; and a rotatable member rotatably mounted on the pivot structure for rotation about a rotational axis spaced radially from the pivot axis by a radius. The rotatable member engages the driving element in a tension applying relationship such that the driving element is tensioned and in reaction applies a hub load force to the rotatable member at an angle with respect to the radius.
The tensioner is mounted on the engine such that when the engine is in the initial condition the pivot structure is angularly positioned at an initial angular position. In this initial angular position, the spring structure applies the tensioning torque to the pivot structure such that the driving element is tensioned to a first mean dynamic tension when the pivot structure is in the initial angular position thereof. As the engine thermally expands! to the hot engine condition, the mean dynamic tension in the driving element increases so that the hub load force applied by the driving element pivots the pivot structure in an opposite direction opposite the tension applying direction away from the initial angular position thereof to a hot engine angular position. The hot engine angular position is spaced from an end of the predetermined range of angular positions in the tension applying direction. The spring structure applies the tensioning torque to the pivot structure such that the driving element is tensioned to a second mean dynamic tension when the pivot structure is in the hot engine angular position thereof. The aforementioned end of the predetermined range may be a point determined by engine manufacturer specifications/requirements, or a maximum travel stop as discussed above. Further, this end of the predetermined range may be the potential tooth skip position in an arrangement wherein no maximum travel stop is used, and the increase in mean dynamic tension necessary to reach this position, which is specified below as being 75% or more greater than the tension at the hot engine angular position, would be set high enough to prevent the pivot structure from moving into this position. This aspect of the invention should not be considered as being limited to a tensioner with a tooth skip position, a stop, or other structures discussed in connection with other aspects of the invention as being determinative of the end of a predetermined range. The spring structure and the initial angular position of the pivot structure are selected such that the mean dynamic tension of the driving element required to pivot the pivot structure in the opposite direction from the hot engine position to the end of the predetermined range continually increases in such a manner that the mean dynamic tension required to pivot structure from the hot engine position to the end of the predetermined range is at least 75% greater than the second mean dynamic tension.
Other objects, features, and advantages of the present application will become appreciated from the following detailed description, the accompanying drawings, and the appended claims.